Follow-up control system



NOV. 26, 1946. OLKEN 311,75

FOLLOW-UP CONTROL SYSTEM Filed Sept. 12, 1941 2 Sheets-Sheet 1 ROTAT-ION(pagan-Q) Hyman O/ken Nov. 26, 1946. H, OLKEN 2,411.759

FOLLOW-UP CONTROL SYSTEM Filed Sept. 12, 1941 2 Sheets-Sheet 2 W mmHyman Ol/(en .32 Fo/lowing f/emem v Patented as. 26, rate 2,411,750FOLLOW-UP- CONTROL SYSTEM Hyman lken,.Washington, D. C.

Application September 12, 1941, Serial No. 410,534

, 12 Claims. 1

This invention relates to control systems and more especially toregulating devices for control systems, wherein an indicator or sendinginstrument controls the position of a following unit or other receivingdevice.

Among the objects of my invention is the provision of an accurate andreliable following unit control system which enables the maintenance ofclose synchronization of movement of indicating and following units,which possesses greater mechanical simplicity, together with greaterefllciency, than heretofore known control systems, which is economicalto construct, requiring a minimum of expensive parts in its production,which is serviced readily without the assistance of a, specially trainedexpert, and which accordingly is adapted for a wider range ofapplication in the art of following unit control.

Other objects in part will be obvious and in part pointed outhereinafter. v

'The invention accordingly consists in the combination of elements,features of construction and arrangement of parts and in theseveralsteps and the relation of each of the same to one or more of theothers as described herein and shown in the accompanying drawings, thescope of the application of which is indicated in the following claims.

In the accompanying drawings illustrating certain features of myinvention,

Figure l diagrammatically illustrates a preferred basiccontrol circuitfor the llowing unit of my invention.

Figure 2 illustrates a motor-driven centralizing device for the controlmechanism of Figure 1.

Figure 3 illustrates first time derivative of deviation following unitdamping mechanism in circuit with the apparatus of Figure 2.

Figure 4 gives a graphic comparison of the operation of certain controldevices described hereinafter.

Figure 5 illustrates velocity squared damping mechanism applied to theapparatus of Figure 2.

Figure 6 illustrates selector mechanism applied to the combined dampingmechanisms of Figs. 3 and 5.

As conducive to a clearer understanding of my invention, it should benoted at this point that control systems of the type described broadlycomprise an indicator, as for example, a galvanometer, a compass. a gunsight or a range finder, which is moved under very little power: and aservo arrangement to effect the high power driving of a following unitin res onse to displacement of the indicating element of the indicator.The following unit comprises, for example, a mount, a turret, a directoror a recorder. The servo arrangement usually comprises a powerful motor,for driving the following unit, and a control, usually an amplifier, torun the motor a proper amount and in a proper direction to reduce tozero any deviation of the following unit from the indicating element.

A control system of the type described, when employed for controlling a,gun mount, enables the automatic pointing of a gun in correspondencewith the direction of a target, as indicated. by a dial setting of arange finder or by a position of a gun sight. Other positioning typeregulators are in use, such as those for positioning a cutting tool of alathe in accordance with the position of a stylus following a templet;or for positioning a recorder pen in accordance with a galvanometerpointer indication. It will be understood that my invention applies toall applications of this'type, but for purposes of illustration, thetheory of gun mount control is stressed to some degree.

Naturally, a heavy following unit being driven under high power has highinertia and this inertia causes the following unit to overshoot aposition signalled by the indicating element. Upon the following unitovershooting signalled position, a corrective action occurs wherein thefollowing unit reverses to reduce its deviation from the indicatingelement. This process of overshooting, then reversing, commonly istermed hunting. Often more than one overshoot and correction take placebefore the following unit comes to rest at proper position.

For most all applications of control systems of the type defined,particularly for gun pointing,

it is desirable to eliminate overshooting and hunting .of the followingunit, or at least to reduce these factors to a tolerable minimum. It isknown in the art that making the following unit motor speed decrease indirect proportion to deviation greatly reduces overshooting and huntingof the following unit. Also, it is known in the art that applying an"anticipating correction" to the following unit motor control systemproportional to the rate of change of deviation between indicatingelement and following unit, thatis, further slowing down the drivingmotor in proportion to the first time derivative of the deviation, willfurther reduce hunting and overshooting 0f the following unit. Stillfurther,- it is known thatupon the application of an additional"anticipating correction," a second time derivative of deii viationreduces, even more, overshooting and hunting of the following unit.

Where most refined control is desired, that is, where only negligiblehunting of the following unit is permissible, it is conventionalpractice for reasons noted hereinbefore, to provide a control systemwherein following unit motor speed is decreased in direct proportion todeviation, and wherein first and second time derivatives of deviationare applied further to damp the motor speed. To make such regulatorseffective, there must be very sensitive indication of the deviation.Anamplifier is used in order to achieve such sensitive indication.Amplification frequently is accomplished by electrical means such as bythe use of radio tubes, or by hydraulic means, or mechanically bystep-up gearing as by using a 36-speed synchro. By amplifying thedeviation by making speed of the following 'unit propor tional todeviation, and applying first and second time derivative corrections tothe motor control system, reduction of deviation to zero is permittedwith negligible hunting or overshoot of the following unit.Amplification, however, spreads a small deviation into a wide operatingrange of the following unit motor controlling mechanism. Therefore,amplification restricts following unit control to a small range ofdeviation, hence to a small interval in the total operating range of thefollowing unit.

In machines having extensive range of operation, such as a gun mountwhere range of train may be up to 360, and possible deviation in trainmay vary through as 'much as 180, it has become the practice to maintainsensitive precise control over the following unit or mount only for asmall range of deviation of about 2 Very accurate first and second timederivative of deviation control, accordingly, is maintained over thefollowing unit when the indicator and following unit are close together.When deviation extends beyond this range, a relay, for example, switchesoff the sensitive control mechanism and the motor of the following unitmerely is turned full on, in proper direction, until deviation againdecreases to 2 at which time the relay terminates full-on operation'ofthe motor and brings into play the sensitive control mechanism.

Such an over-all method of control has the serious objection that themechanism for deriving a second time derivative of deviation andsuperimposing it properly upon the first derivative correction, whetherby electrical, mechanical or hydraulic means. makes for an intricateapparatus which is costly to manufacture, which gets out of orderreadily, and which require specialized experts to understand and serviceit. Even more important is the fact that in machines where swings of theindicating element, hence deviations, are large, as in positioning anantiaircraft gun, there is but hit-.or-miss control of the gun over thegreatest partof the range of movement. When gun and indicator or sightcome very close together, that is, when deviation becomes small, there ia sudden switching and jumping over to precise first and secondderivative control. If the overshoot extends beyond the fine controlrange, there is again a sudden switch-over back to full-on operation ofthe motor. This results not only in poor aiming of the gun, but thesudden transitions from full-on operation to sensitive control make itadditionally difl'icult to provide smooth control over the movement ofthe gun.

One object of the present. invention, therefore,

is the provision of following unit control apparatus which ensures welldamped asymptotic approach of the following unit to indicated position,which is adapted to apply one of two following unit speed corrections tothe following unit motor depending on the degree of deviation betweenthe following unit and indicating element, which for large deviationsdamps the following unit motor by the imposition of a velocity squaredspeed correction and which applies a time derivative of deviationcorrection to the motor for small deviations giving refined control tothe motor and thus to the following unit as the following unitapproaches indicated position.

Referring now more particularly to the practice of my invention, Iprovide a control system wherein movement of an indicator and afollowing unit are so synchronized that displacement of the indicatorfrom a neutral position brings about proportional displacement of thefollowing unit. In my control system, I provide means for starting therestoring motor in proper direction so as to reduce deviation to zero,when there is deviation; and mean for shutting off the restoring motorwhen deviation is reduced to zero. I also employ the conventionalpractice of making the motor speed decrease proportionally as thedeviation decreases, and of putting in, in addition, a first derivativecorrection for motor velocity.

I apply the first derivative correction over only a very small portionof the total operating range of my control system. A superimposed secondderivative correction also may be present within this range, even thoughI attain good results without any such correction. This range is sosmall that with first derivative'correction only,

'hu'nting, overshootingand residual deviation of the following unit arenegligible.

Beyond that range, I apply no derivative correction of any kind, but acorrection proportional to the square of the velocity of the followingunit. This prevents storage of ener y in the following unit on bigswings in a manner linear with deviation. Consequently, as the deviationbecomes small, the following unit has very little stored energy and canbe stopped substantially at proper position by the first derivativecorrection control alone.

For switching over automatically from the first derivative control tovelocity squared correction, or vice versa, when the deviation becomeslarge or small as the case may be, I use a predetermined ratio ofunbalance of restoring motor control elements. These restoring motorcontrol elements are, for example, opposed motor fields. or opposedhydraulic means. This method of automatic switching makes for apositive, snap-like switch-over as distinguished from a chatter,trembling, slow transition.

My entire system of control eliminates the intricacy of secondderivative elements, and particularly as applied in my preferredembodiment, makes a rugged, reliable unit sufficiently compact andsimple to construct, install and maintain without great expense andwithout requiring the aid of high-skilled technicians.

As illustrative of the practice of my invention, attention is directedto Fig. 1 'of the drawings, wherein an embodiment of the basicdirectioning unit of my invention is illustrated diagrammatically. Acathode-ray tube T is energized from a battery B, and the tube, in turn,energizes field windings FI and F2 of following unit motor 21. Aninstrument pointer or indicating element l2 ground at l9.

operated in any desired-manner, is mounted piv- Cathode l5, locatedwithin tube T between and 'inalignment with electrodes l3 and I4, isconnected by lead 2l to the midpoint 23 of battery B and' grounded atl9. 4

There are two anode plates, PI and P2 mounted respectively at oppositeends of and within tube T at-points substantially equidistant fromcathode- IS. A circuit is traced from midpoint 23 of 'batteryvB, lead 2lto cathode l5, across tube T to anod plate P2, lead 28, acrossmotorfield winding F2 of the following unit and lead l1 to positiveterminal 26 of battery B. A second. circuit is traced from midpoint 23of battery B,

lead 2| to cathode l5, across tube T to anode plate Pl, lead it, acrossmotor field winding Fl of the following unit and lead H to positive'terminal 26 of battery B.

In the present embodiment of my invention, I apply the principle thatcathode raysare repelled or deflected by external charges of negativeelectricity. This principle is employed more particularly in controllingthe driving of motor 21 of the following unit. Cathode beams or rays Bl,B2, passing from cathode l5 to plates Pl and P2, respectively, arecontrolled by electrodes l3 and H charged with ".he same high potentialnegative electricity. Normally the instrument pointer orindicatingelement l2, carrying elecposition, cathode l5 and electrodesl3 and I4 are in alignment. Upon the indicating element l2 being atcentral position, electron beams BI and B2 come equally into focus uponplates Pl and P2, respectively. This is understoodmore clearly byobserving that cathode I5 is connected through lead 2| and midpoint ofbattery B to Electron beams Bl and B2 of equal intensity pass fromcathode IE to anode plates PI and P2. respectively. Current flows in thecircuit traced from anode plate P2, through.

B, is greater than the current flowing through winding F2 in circuitwith plate P2. A current differential therefore exists between the twoopposed windings Fl and F2 and motor 21 is energized by thisdifferential. It should be noted at. this point that when indicatingelement l2 moves on the right side of central position, the distance ofelectrode I?! from center and the downward deflection of beam B2 fromanode plate P2 by electrode l3, increase in direct proportion. It is tobe noted further that current flowing through field winding F2, or thecircuit of plate P2, and the distance of electrode l3 from centralposition, on the right side of central position, increase in inverseorder,'until, of course, all of beam B2 is deflected from plate P2.Since electron beam Bl substantially is unaffected by any movement ofelectrode l3 to the right, plate current in the circuit of plate Pl andfleld winding Fl remains substantially constant. It follows, then, thatfor movement of the indicating element l2 on the right side of centralposition, the

distance of electrode l3 from central position representing themagnitude of deviation between the indicating element and the followingunit, the unbalance of the currents in fleld windings FI and F2, and thevelocity of motor 21 of the following unit, allincrease in directproportion.

. trode l3, rests at central position, at which lead 28, field windingF2 and lead l1 to positive terminal 26 of battery B. 'At the same time,a substantially equal current flows in the circuit traced from plate Plthrough lead l6, across a ,motor fleld winding Fl, and lead l1 topositive terminal 26 of battery .3. Thus the opposed windings Fl and F2,forming the fleld motor 21 of the following unit, carry equal currentssince they are in the plate circuits of tube T, and there is no currentdifferential to driv fol lowing unit motor 21.

When negative electrode I3 is moved to the right of central position bycounterclockwise rotation of indicating element l2 about point l0,electron beam B2 is repelled by electrode l3 and part of the beam nolonger strikes plate P2. Current flowing in the circuit traced fromplate P2 through lead 28, fleld winding F2 and lead "to batteryBfaccordin ly, is decreased. Meanwhile, electron beam Bl still isfocused in its substantial entirety upon plate Pl with the result thatcurrent flowing through the circuit defined by lead It, fleld winding Fland lead l1 to battery On the other hand, when electrode l3 moves to-.the left side of central position, plate current in thecircuit ofplate P2 and fleld winding F2 remains substantially constant. Until allof beam -BI is deflected below. plate PI by electrode 13,

the current flowing through Fl increases inversely as the displacementdistance of'electrode l3 to the left of central position; it follows,therefore, that as displacement of electrode l3 to the left of centralposition increases, current unbalance in the windings FI and F2 and thespeed of the motor 21 of the following unit both increaseproportionately. I

Movement of indicating element l 2 to the right of central'positioncauses a greater current to flow through winding Fl than in F2. On theother hand, deflection of indicating element l2 to the left of centralposition causes a predominating current to flow through winding F2;Accordingly, it can be seen that driving motor 21 reverses when theindicating element crosses central position. The reversible drivingmotor is of sumcient horsepower to position the following unit asindicated by the signal or current differential created by thedeflection of indicating element l2. For training large turrets,whichrequires more than several horsepower, reversible motor 21 could beadapted to control a motor of much greater power, as, forexample,through a relay system, to position the turret correctly.

The above description details one essential element of my invention andis a device for producing a speed of 'the following unit driving motorproportional to the deviation. I prefer the above embodiment, but othersknown in the art may be used.

In addition to the above element, 1 incorporate an element which stopsthe following unit driving motor, and thus the following unit, when thedeviation has reached zero. One embodiment of this is as follows: It isto be observed from Fig. 1 that where indicating element l2 moves awayfrom central position, driving motor 21 is driven by the unbalancedcurrents coursing through fleld following unit motor and the motor stopswhen central position is reached. In order to stop the following unitmotor when the deviation between following unit and indicating elementl2 has reached zero, reset mechanism is provided as illustrated in Fig.2. My basic following unit control circuit described with reference toFig. 1, also is employed in the control mechanism illustrated in Fig. 2.In addition, driving motor 2'! drives a following element through shaft30, gear 3| and ear 32, at a velocity in fixed ratio to motor velocity.A reset disc 35 to which cathode ray tube T is aflixed, is driven by themotor 21 through shaft 29, bevelled gear 38 mounted on shaft 29,bevelled gear 31 mounted on worm shaft 33, Worm shaft 33, worm gear 34and gear teeth 36 or disc 35.

In operation, assume that indicating element l2 moves to a signalpostion on the left side of its central position, thereby creating adeviation between the following unit and the indicating element.Electron beam Bl is deflected downward an amount proportionate to thedisplacement of the indicating element or to the deviation of thefollowing unit. Current flowing in the plate circuit traced from anodeplat Pl, through lead l6 across winding Fl, and lead I! to positiveterminal 26 of battery B, accordingly is decreased. Meanwhile electronbeam B2 remains in substantially full focus upon anode plate P2 and apredominating current flows in the plate circuit traced from P2 throughlead 28, across winding F2 and lead I! to positive terminal 26 ofbattery B. The unbalanced currents flowing in the plate circuitsof'plates PI and P2 cause following unit motor 21 to drive'reset disc35. As following unit motor 21 continues to drive, reset disc 35 andcathode ray tube T rotate at a decreasing rate in a counterclockwisedirection; thus, electrode l4 and cathode l are rotated gradually towardcentral position, that is, to alignment with electrode l3 on indicatingelement l2.- The follow-.

ing unit motor also drives'the following unit so as to overcome thedeviation existing between the following unit and indicating element'l2. By rotating the electron tube '1, the effect of electrode [3 on beamBl gradually decreases with the result that more and more of electronbeam Bl falls into focus upon plate Pl. Since electron beam B2remainssubstantially in complete focus upon plate P2 throughout thecounterclockwise rotation of reset disc 35, the current in the circuitof plate P2 and windin F2 remains high and substantially constant. Onthe other hand, current flowing in the circuit of plate PI and followingunit motor field winding Fl gradually increases with the rotation ofreset disc 35 and the unbalance of currents flowing through windings Fland F2 diminishes slowly until an actua1 balance of currents is obtainedand following unit motor 21 comes to rest. It can be seen, therefore,that currents through field windings Fl and F2 tend more and more tobalance as the deviation of the following unit from the indicating element l2 decreases. Currents in field windings Fl and F2 approachbalanced condition as deviation between indicating element and followingunit decreases. It follows, then, that motor velocity is proportional tothe deviation and decreases proportionately with the deviation.

After the following unit has come to rest from the last signal, assumenow that indicating element l2 and electrode l3 are moved to the rightof central position with respect to cathode ray tube T. Electron beam B2is deflected downward an amount proportionate to the displacement ofconstant.

8 electrode l3 from central position. Current flowing in the circuitdefined by plate P2, lead 28, winding F2 and lead H to battery B,accordingly is decreased. Movement of electrode l3 to the .right haslittle effect upon electron beam Bl which, therefore, remains in focusfully upon anode plate Pl. The current flowing in the circuit defined byplate Pl, lead l6, winding Fl, and lead I! to battery B, remains highand substantially A predominating current, therefore, flows in thecircuit of plate P2, and winding Fl, and following unit motor 2'! startsdriving in an opposite direction as compared to the direction ofresponse of the motor to a current unbalance set up by movement ofelectrode l3 to the left of central position. At the same time, motor 21begins driving reset disc 35 and cathode ray tube T in a clockwisedirection and electrode l4 and cathode l5 slowly approach alignment withelectrode l3. The deflecting effect of electrode l3 upon electron beamB2 slowly diminishes, and as this occurs, beam B2 rises slowly, comingmore and more into focus upon anode plate P2. Current through thecircuit of plate P2, including following unit motor field winding F2,gradually increases and finallycomes into balance with current flowingthrough winding Fl, in the circuit of plate Pl, when the tube T reachescentral posi- -tion with respect to electrode l3. Since balanced platecurrents coursing through windings Fl and F2 leave no differential ofcurrent to drive the Again it must-be observed that currents throughfield windings Fl and F2 tend more and more to balanceas the deviationof the following unit from indicating element l2 decreases. As before,currents and field windings Fl and F2 linearly approach balancedcondition as deviation between indicating element and following unitdecreases. It'followsonce more that motor speed decreasesproportionately with the deviation.

With the reversible basic motor control circuit and reset mechanismdescribed hereinbefore,-displacement of indicating element l2 fromcentral position in 'either directiondecreases with proper rotation ofcathode ray tube T and the speed of the following unit also decreases.The motor 21 acordingly,is eased to a halt as cathode ray tube T isrotated to central position with respect to in dicating element l2.

As plate currents in Fl and F2 become balanced, it is possible thatinertia gained by the following unit while driven to signal position, ata velocity in ratio to motor velocity, by motor 21, will cause resetdisc 35 and tube T to rotate beyond signal position. When this occurs,tube T is rotated beyond central position with respect to indicatingelement l2.

overshooting of the following unit, and the following unit motor 21reverses in response to the overshooting. As a result, the followingunit oscillates or hunts about the point where it should come to rest.

In short, I have described above embodiments of a speed-proportional-todeviation device, and

a reset device, to stop the motor at deviation zero. I

Other embodiments may be used. But both these elements may not be enoughunder given operating conditions. Therefore, I apply in addition, afirst derivative correction, one novel embodiment of which is asfollows:- Referringnow more particularly to Fig. 3, it will be notedthat I connect a variable resistance45 across-tube plates Currents inwindings- Fl and F2, accordingly, become unbalanced by 1 in the platecircuit of plate PI.

acrimo PI and P2 and across field windings FI and F2 of the followingunit motor 21. These connec:-

tions are traced from plate PI acrosslead I5 upto junction 40 of windingFI, thence over leads 42 and 45,'across variable resistance 45, lead M.

to junction 48 of winding F2 and lead' 28 toplate P2. I connectcondenser 43 across resistance 45,

' illustrated in Fig. 4, wherein rotation of the lowing unit-is plottedin the ordinate against a time of rotation abscissa. Curve A representswhich connection is traced from point 41, lead 45,

condenser 43', selector 44 to resistance 48.

Now it must be noted that the distance ofin- .dicating element I2 fromcentral position and the differential of voltage across the circuits of.of voltage change between the plate circuits PI and P2 and thereforealso is proportional to the rate of change of deviation between thefollowing unit and the indicating element I2.

To illustrate how the following unit motor 21 is damped by thecorrection current discharged by condenser 43, assume that indicatingelement I2 is deflected to the left of central position.

' Electron beam BI in part is repelled from plate PI by negativeelectrode I3, and current decreases plate circuit .of plate P2 remainssubstantially unafiectd by deflection of electron beam BI. Therefore,more current flows in field winding F2 than in winding Fl and followingunit motor 2! begins driving the followin mechanism, in proportion tothe deflection of indicating element I2, that is, in proportion to thedeviation of the following unit.- Reset disc 35 and tube '1 are drivenin a. counterclockwise direction by motor 21 and the deviation of thefollowing unit from indicating element I2 gradually decreases, asdescribed more fully with reference to Fig. 2. Meanwhile, currentdischarges from the circuit of plate P2 across condenser 43 andresistance 45,

into the circuit of plate PI and the unbalance of currents flowingthrough field windings FI and F2, accordingly, decreases. It must beremembered that the correction current flowing across condenser 43 ishigh when indicating element I2 is first moved to left position, and thefollowing unit, reset disc 35 and tube Tare moving toward signalposition at high velocity. The applied correction current isproportional to the rate of change of deviation between the followingunit and the indicating element. As reset disc 35 and tube T are drivenby motor 21 to central Current in the following unitapproach to a givensignal position of indicating element I2, when mydampin currentcorrection proportional to the rate of change of deviation is applied toone of the following unit motor windings FI- and F2. Curve B shows themanner in which a following unit control system having no correctioncurrent permits hunting of the following unit about a fixed signalposition. Curve B, therefore, represents the operation of such apparatusas is disclosed in Fig. 2 where no overshooting correction is appliedand the speed-of the following unit motor is roportional to thedeviation between following unit and indicating element. Curve Cillustrates following unit approach to signalled position when a motorcontrol system comprising complicated superimposed first and secondderivative motor damping means is employed.

- The variable resistance element 45 permits ready adjustment of thecorrection current draining through condenser 43 and thus, my controldevice can be regulated to ensure welldamped, asymptoticapproach of thefollowing unit to signalled position under different types of workingconditions.

Now, where following .unit control mechanism is needed for controlling afollowing unit responding to predominantly small signals at lowvelocit). particularly where friction and other factors preventconstant, acceleration of the following unit, a correction of the firstderivative typ just described. is adequate to produce well-dampedapproach of the following unit to signalled position. When largersignals, and consequently,

" larger velocities 'of the following unit are enposition with respectto indicating element I2,

the speed of motor 21, as described with reference to Fig. 2, decreases,and the correction current across condenser 43, accordingly, decreases,but

this correction current, nevertheless remains countered, or when thefollowing unit is heavy,

. negligible at such velocities and acceleration relatively is constant.I find, therefore, where the deviations are large, that an overshootanticlpation correction applied to the following unit motor inproportion to the square of following unit velocity gives a-more nearlyasymptotic approach of the following unit to signalled position. Oneembodiment of my invention, in accordance with this principle, isillustrated in Fig. 5 of the drawings.

It will be noted in Fig. 5, that my basic following unit motor controlcircuit and reset mechanism described more particularly with referenceto Fig. 2, are shown in combination with overshooting control apparatus.My overshooting control apparatus is provided with a shaft 50 extendingfrom following unit motor 21 which shaft is mounted in bearing 5|. Atthe end of shaft 50, remote from motor 21, is mounted a watt-meter typemagnet 52. A shaft 57 supported in bearings 54 extends coaxially fromshaft 50. Disc 58 is secured to the end of shaft 51 and is free torevolve in the gap of magnet 52. Meter-type coil springs are attached toshaft 51 and to bearings 54 to retard rotation of disc 5i! in eitherdirection. Upon driving the following unit as described moreparticularly with reference to Fig. 2 of the drawings, shaft 50 andmagnet 52 rotate in ratio with the following unit motor. Magnet 52exerts a drag upon the conducting disc 58, and the disc, accordingly,re-

fol-

volves an angular distance proportional to the velocity of followingunit motor 21.

Rotary-type variable resistor 59, wound according to a square-law orcurrent square taper, has a contact arm 56 fastened to disc 58 at point65. Field windings Fl and F2 of motor 21 are connected across variableresistor 59. One cir- 12 velocity of the motor and thus that of theratio driven following element are decreased gradually by a slowbalancing of plate currents is the circuit is traced from battery 6!,over lead 62, lead l1, across field winding -Fl, lead 64, resistor 59,contact arm 56, lead 51, variable resistor 66 and lead 66 back tobattery 6|. Another circuit is traced from battery 6!, over lead 62,across field winding F2, lead 58, across variable resistor 59, contactarm 56, lead 61, variable resistor 60 and lead 66 back to battery 6l.

While following unit motor 21 is at rest, contact arm 56 remains atposition 55 on the variable resistor 59, and equal, but opposed currentsflow from battery 6i through resistor 59 and field windings Fl and F2. 7

Upon indicating element l2 being deflected to the left of centralposition, a predominating current fiows in the circuit of plate P2 andfield winding F2, as described more particularly hereinbefore. Motor 21drives at a velocity proportional to the displacement-f indicatingelement l2 from central position, that is, proportional to the deviationbetween indicating element l2 and the following unit. At the same time,reset disc 35 and tube T are driven in a counterclockwise directionthrough gearing 36 and 34 shaft 33, gearing 31 and 38 and shaft 29 byfollowing unit motor 21. The velocity at which the reset mechanism isdriven by motor 21 also is proportional to following unit deviation orto the displacement of indicating element l2 from central position.Consequently, as the reset mechanism is driven toward central or neutralposition, the velocity of the following unit decreases.

With the initial movement of indicating element l2 to left of centralposition, following unit motor 21 starts driving shaft 50 and magnet 52at a velocity in proportion to the signal. Magnet 52 exerts a drag upondisc 58, and the disc along with shaft 51 and contact arm 56 rotate inproportion to magnet speed. Contact arm 56 is dis-' placed, in theproper direction; from its neutral position 55 to vary the resistanceacross resistor 59.. Resistance to the current flowing from bat- 'tery6| across field winding Fl, accordingly, is

decreased. The potential of plates PI and P2 across windings Fl and F2,therefore, decreases j and this results in a decrease current drivingfollowing unit motor 21.

It must be recalled that velocity of following unit motor 21 and thusthe velocity of the motor driven following element are reduced primarilyby reset disc 35 and cathode ray tube T being driven in acounterclockwise direction toward central position with respect toindicating element [2. As following unit motor velocity is decreased bythe reset mechanism, the energy correction current coursing from battery6| across variable resistor 59 and field winding Fl also decreases. Thisdecrease of correction current occurs because the resistance acrossresistor 59 increases in direct proportion with decreasing followingunit motor velocity. Since resistor 59 has a square law current taper,the current flowing across it to field winding Fl varies in directproportion to the square of the velocity of the following unit motor.The ratio of current to velocity is varied'by adjustment of variableresistor 60.

It is to be understood clearly, therefore; that cuits of plates, PI andP2. This is accomplished by the reset mechanism of which the motor andreset disc 35 are parts. The motor stops when central position of thereset mechanism is reached. Throughout the period of gradual decrease orincrease of following unit motor velocity, a correction current isapplied'across resistor 59 to one of field windings Fl and F2, toprevent the following unit from overrunning signalled position. Thiscorrection current varies in direct proportion with the square offollowing unit velocity, and is applied to decrease unbalance ofcurrents between windings Fl and F2 in accordance with a velocity squarelaw, until the following unit motor comes to a well-damped rest, atwhich time there is once more a complete balance of currents in thefield windings of the motor. When indicating element I2 is moved to theright of central position, it will, of ourse, be understood that myapparatus functions in a fashion similar to that just outlined, exceptthat motor 21 reverses and the correction current is applied throughresistor 59 across field winding F2.

Fig. 6 of the drawings illustrates following unit control apparatuscomprisin a combination of the two following unit overshoot-preventingcontrol systems more specifically described hereinbefore. As thefollowing unit motor responds to large signals, I prefer to use a motorcontrol system of the type illustrated in Fig. 5, with which anovershoot anticipation correction is applied in ratio to and directlyproportional to following unit velocity squared. When the following unitmotor responds to small signals, I prefer to employ a motorcontrol'system of the type more specifically described with reference toFig. 3, wherein an overshoot anticipating correction currentproportional to the rate of change of deviaion between the followingunit and indicating element I2 is applied to the fo lowing unit motor.For detailed operation of the respective mechanisms, reference is mademore particularly to the previous description herein of Figs. 3 and 5.In accordance with the present embodiment of my invention, I connect anelectrical quotient meter 10 across plates PI and P2 of a cathode raytube of the type described hereinbefore. The electrical quotient meter10 operates on the ratio of the two plate currents of plates PI and P2.A spring-restrained indicator shaft 15 driven by meter 10 carries switchelements I8 and 19. When following unit motor 21 is not operating, orwhen a small potential exists across field windings FI and F2 of thismotor, switch element 19 closes the circuitacross contacts I6, l1 and amotor overshoot anticipating system'of the type described with referenceto Fig. 3, is brought into operation. Therefore when the motor isoperated by a small current differential, a correction current,

proportional to the rate of change of deviation between the followingunit and indicatin element [2, therefore, is applied to one of the fieldI or the power ratio of these currents, exceeds a predetermined amount,requiring that the following unit be driven more than 2 /2", forexampie,by the following unit motor to reduce fol-' lowing unit deviation tozero. Meter turns spring-restrained shaft in one direction or the other,depending upon which plate circuit of plates PI and P2 carries thelowest current.

Switch element 18 closes either a circuit acrossapplies a correctioncurrent proportional to the I rate of change of deviation between thefollowing unit and indicating element-12,.to one of the field windingsFl, F2 of motor 21. As reset mechanism and the following unit of thetype described in Figs. 2 and 5 are driven toward central position orsignalled position, it will be noted, by particular-reference to thedescription of Figs. 2 and 5, that velocity of the following unit motor21, and the velocity of the following element which is in ratio to motorvelocity, accordingly, decrease in direct proportion to the magnitude ofthe deviation. A damping current, however, is applied to reduce motorfield current unbalance in proportion to the square of the motor orfollowing unit velocity, as described more particularly with referenceto Fig. 5. When signal current differential of the plates PI and P2decreases to the predetermined amount or ratio, as, for example, whenfollowing unit deviation is reduced to the predetermined deviationof 2springloaded shaft 15 overcomes the torque exerted by meter 10 andswitch element 18 rotates away from contacts ll, 12 or contacts I3, 14,as the case may be, cutting out the motor overshoot preventing system ofthe velocity-squared type. Meanwhile, switch element 19 closes a circuitacross contacts l6, l1 and the overshoot preventing system describedmore particularly with reference to Fig. 3, functioning in directproportion to the rate of change of following unit deviation comes intooperation. Therefore, a refined correction current proportional to therate of change of deviation is applied to one of the field windings FIand F2, until following unit motor 21 and the following unit are broughtto a well-damped stop by the reset mechanism and basic control circuit,more particularly described with reference to Figs. 1 and 2:

I find that thebasic control system of my invention, one embodiment ofwhich is illustrated in Fig. 2 of the drawings, is mechanically simpleand economical to construct. The system is highly sensitive to movementof the signalling or indicating element giving a signal which variesaccurately in direct proportion to the deviation of the following unitfrom the indicating element. It is to be understood quite clearly thatthe unbalanced currents fiowing across my cathode ray tube system may beapplied in numerous ways to drive the following unit motor, the opposedmotor fields described herein being one illustration. Instead of drivingthe following unit motor directly, it is to be further understood thatthe unbalanced plate currents may be used to operate a relay system forcontrolling larger currents or a larger motor.

Either my following unit control system which operates in proportion tothe rate of change of following unit deviation, or my system whichoperates in proportion tothe square of the following unit velocity, maybe used separately with i4 J good results under certain circumstances.More-s over, a following unit motor overshoot preventing systemcomprising a first time derivative of de-..-. viation control means anda velocity square control means for applying corrections to thefollowing unit motor, with means for switching automatically from one ofthese controls to the other, has a wide range of application inthe'remote' control art. With the latter combination, overshooting ofsignalled position by the following unit is prevented whether thefollowing unit is heavy or light, or whether the velocity of thefollowing unit is high or low.

It is to be understood quite clearly that my basic control orintermediate control system is not limitedto an electrical device.Mechanical,

or hydraulic means, for example, may be employed to control followingunit motor speed in proportion to the deviation existing between thefollowing unit and the indicating element. Moreover, other mechanism,including mechanical or hydraulic means,'for example, maybe employed toapply the first derivative of deviation correction, or .thevelocity-square correction to the following unit in order to maintainovershooting and hunting at a minimum. Where the first time derivativeof deviation correction and the velocity-square correction are appliedin sequence, automatic switchover from one correction to the other maybe accomplished by apparatus which responds to a particular power limitor to a particular ratio or unbalance of power driving the followingunit. The switchover apparatus 'may be of mechanical, electrical orhydraulic type, for example, without departing from the spirit of myinvention.

My invention has valuable application also to control systems forcontrolling process conditions, such as temperature, salinity and thelike. For these applications, a pyrcmeter pointer, salinity meterpointer or the like serves as the indicating element. Thefollowing unitis a recorder motor or just a motor alone, made powerful enough to drivea low-inertia valvefor' controlling the flow of medium to restore adesired process condition. The deviation of the motor from desiredprocess condition, accordingly, is reduced automatically to zero. Themotor provided is so powerful that its inertia is the predominantcharacteristic to be controlled rather than the negligible inertia ofthe valve. By applying my principle of first time derivative ofdeviation motor control and switching automatically, to velocity squaredcorrection on large deviations, a desired process condition will beapproached asymptotically, as in controlling amount, without overshootor hunting. This is particularly valuable in processes where largebatches of material are dumped into the process suddenly. Say, forexample, a batch of cold milk is dumped into a pasteurizing tank. Asudden fluctuation in controlled temperature condition occurs, and theregulator, when coupled with a pasteurizing tank thermometer and. asteam heat supply valve of' the tank, gives an asymptotic restoration oftank temperature to desired value. Similarly, good results are achievedwhen my control system is employed for controlling conditions such ashumidity, pressure, liquid, level, rate of flow of fluids orelectricity, voltage, frequency and the like.

As many possible embodiments may of my invention and as many changes maybe be made is to be interpreted as illustrative and not in a 'limitingsense.

- squared to reduce following unit energy and means for applying afirsttime derivative of deviation correction to the driving motor toreduce the energy of the motor-when said deviation decreases to a smallamount.

2. A control system of the class described, comprising, in combination,an indicating element adapted to be moved to produce a deviation betweenit anda following unit, the latter having as an element thereof adriving motor for reducing deviation of said unit from said indicatingelement, means for energizing said driving motor,

means for maintaining the velocity of the driving motor proportional tothe magnitude of the deviation of the following unit from saidindicator, means for applying a correction to the driving motorproportional to motor velocity-squared to reduce following unitvelocity, means for applying a first time derivative of deviationcorrec- "'on to the driving motor to reduce the velocity or the motorwhen said deviation decreases to a small amount, aid automatic means forswitching from one correction applying means to the other. I

3. A control system of the class described, comprising, in combination,an indicating element adapted to be moved to produce a deviation betweenit and a following unit, the latter having as an element thereof areversible driving motor for reducing deviation of said unit from saidindicating element, means for energizing said driving motor, unbalancedpower means for maintaining the velocity of the driving motorproportional to the magnitude of the deviation of the following unitfrom said indicatonmeans for applying a.

correction to the driving motor proportional to motor velocity squaredto reduce following unit energy, means for applying a first timederivative of deviation correction to the driving motor to reduce thevelocity of the motor when said deviation decreases to a small amount,and automatic switching .means operated by said unbalanced power meansto switch out one of said correction applying means and to switch on theother thereof, v

4. .A control system of the class described, comprising, in combination,an indicating element adapted to be moved to produce a deviation betweenit and a following unit, the latter having as an element thereof adriving motor for reducing deviation of said unit from said indicatingelement, opposed energizing means which when unbalanced drives saidmotor, means for producing a degree of unbalance between said opposedenergizing means proportional'to the magnitude of the deviation, meansdriven by said driving motor for ,stop'ping the motor at zero deviation,means for applying a correction to the driving motor proportional tomotor velocity squared to reduce followingunit energy; means forapplying a, first time derivative of deviation correction to the drivingmotor to reduce the motor velocity,when said deviation decreases to asmall amount, and automatic switching means associated with said opposedenergizing means to switch out one of the correction applying means andto switch on the other thereof.

5. A control system of the type described, comprising, in combination,an indicating element adapted to be moved to produce a deviation betweenit and a following unit, the latter having as an element thereof adriving motor for reducing deviation of said unit from said indicatingelement, two opposed motor fields for the driving motor, means forproducing a degree of unbalance between said motor fields proportionalto the magnitude of the deviation, means driven by said driving motorfor stopping the motor at zero deviation,means for applying a correctionto the driving motor proportional to motor velocity squared to reducefollowing unit energy; means for ap plying a first time derivative ofdeviation correction to the driving motor to reduce the motor ve- 6, Acontrol system of the class described, comprising, in combination, anindicating element adapted to be moved to produce a deviation between itand a following unit, the latter having as an element thereof a drivinmotor for reducing at a decreasing rate deviation of said unit from saidindicating element, two opposed motor fields for driving the motor,means for maintaining a degree of unbalance of currents across saidmotor fields proportional to the magnitude of the deviation, meansdriven by said driving motor for stopping the motor, means connectedacross said unbalanced motor fields for supplying an anticipatingcorrection current to the driving motor in proportion to the rate ofchange of deviation; means associated with said motor fields forsupplying a correction current to the driving motor proportional to thesquare of driving motor velocity, switch means associated with each ofsaid correction current supplying means, and a current ratio meteroperatingon the ratio of unbalanced motor field currents for so actuatinsaid switch means that one of said correction current supplying means isswitched on and the other switched off upon the departure of unbalancedcurrents from apredetermined ratio. I

7. A control system of the type described, co prising, in combination,an indicating element adapted to be moved to produce a deviation betweenit and a following unit, the latter'having as an element thereof adriving motor for reducing deviation of said following unit fromsaiddisplaceable indicating element; field windings for said drivingmotor; an electrontube having two anode plates connected across saiddriving motor field windings; a cathode disposed adjacent to saidelectron tube anode plates; a source of energy so connected to the anodeplates and 'tube cathode that an electron beam flows between saidcathode and each of the anode plates; said displaceable indicatingelement 'being so connected to the source of energy and so disposedadjacent to said tube cathode that upon displacement, the indicatingelement deflects one of the electron beams causing a motor energizingplate current difierential across said driving motor field windingscating element being so connected to the source of energy and sodisposed adjacent to said tube cathode that upon displacement theindicating ing deviation of said following unit from said between thefollowing unit and indicating ,ele-

ment across said driving motor field windings whereby the driving motoris energized in proportion to said deviation; and a square law variableresistance circuit connected across said tube anode plates fordecreasing following unit energy when plate current differential exceedsa predetermined amount.

11. A control system of the type described comprising an indicatingelement adapted to be moved to produce a deviation between it and afollowing unit, the latter'having as an element thereof a drivingmotorfor reducing deviation of said element deflects one of the electronbeamscausmotor, an electron tubehaving two anode plates connected acrosssaid driving motor field windings, a cathode disposed adjacent tosaidelectron tube anode plates, a source of energy so connected to the anodeplates and tube cathode that an electron beam flows between said cathodeand each of the anode plates, said indicating element being connected tothe source of energy and so disposed adjacent to said tube cathode thatupon displacement the indicating element deflects one of the electronbeamscau'sing a motor energizing plate current differential across saidmotor field windings proportional to the deviation between the followingunit and indicating element; and a condenser leakage circuit connectedacross unit from said displaceable indicating element,

field windings for said drivin motor, a control circuit for supplyingbalanced currents across said driving motor field windings, adisplaceable indicating element for unbalancing in proportion to thedeviation between the following unit and the indicating element thecurrents flowing through said driving motor field windings therebycausing energization of said driving motor in direct proportion todeviation between the following unit and said indicating element,aleakage circuit connected across said driving motor field windingsfordecreasing the nbalance of field currents in proportion to the rate ofchange of deviation of the following unit, a square law variable currentresistance circuit connected across said driving motor field windin sfor decreasing the unbalance of field currents in proportion to thesquare of following unit velocity,

' switchwmeans in each of. said current unbalance prising, incombination, an indicating element said tube anodeplates for decreasingthe plate current differential in proportion to the rate of change ofsaid deviation.

10. A control system of the type described, comprising, in combination,an indicating element adapted to be moved to produce a deviation be-,

tween it and a following unit, the latter having as an element thereof adriving motor for reducing deviation of said unit from said displaceableindicating element; field windings for said driving motor; an electrontube having two anode plates connected across said driving motor fieldwindings, a cathode disposed adjacent to said electron tube anodeplates, 9, source of energy so connected to the anode plates and tubecathode that an electron beam fiows between said cathode and each of theanode plates, a displaceable indicating element connected to the sourceof energy and so disposed adjacent to said tube cathode that upondisplacement said indicating element defiects one of the electron beamscausinga plate opening one of said switchesad current differentialproportional to the deviation -adapted to be moved. to produce adeviation between it and a following unit, the latter having as anelement thereof a driving motor for reducing-deviation of said unit fromsaid displaceable indicating element, field windings for said drivingmotor, an electron tube having two anode plates connected across saiddriving motor field windings, a cathode disposed between said electrontube anode plates, a source of energy so con- 4 nected to the anodeplates and tube cathode that an electron beam flows between-said cathodeand each of the anode plates, a displaceable indicating elementconnected .to the source of energy and so disposed adj acent to saidtubecathode that upon displacement said indicating element defiects one ofthe electron beams causin a motor energizing plate current differentialproportional to the deviation between the following unit and indicatingelementacross said driving motor field windings, proportional todeviation between the following unit and said indicating element, aleakage circuit connected across said tube anode plates for decreasingthe unbalance of plate currents in proportion to the rate of change ofdeviation of th following unit, a square law variable current resistancecircuit connected across said tube anode plates for decreasing theunbalance of plate currents in' proportion to the square of followingunit velocity and switch means in each of said current unbal-

